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Latent heat thermal energy storage is an attractive technique as it can provide higher energy storage density than conventional heat energy storage systems and has the capability to store heat of fusion at a constant (or a near constant) temperature corresponding to the phase transition temperature of the phase change material (PCM). This paper provides a state-of-theart review on phase change materials (PCMs) and their applications for heating, cooling and electricity generation according to their working temperature ranges from (-20℃ to +200℃). Four working temperature ranges are considered in this review: 1) the low temperature range from (-20℃ to +5℃) where the PCMs are typically used for domestic and commercial refrigeration; 2) the medium low temperature range from (+5℃ to +40℃) where the PCMs are typically applied for heating and cooling applications in buildings; 3) the medium temperature range for solar based heating, hot water and electronic applications from (+40℃ to +80℃); and 4) the high temperature range from (+80℃ to +200℃) for absorption cooling, waste heat recovery and electricity generation. Different types of phase change materials applied to each temperature range are reviewed and discussed, in terms of the performance, heat transfer enhancement technique, environmental impact and economic analysis. The review shows that, energy saving of up to 12% can be achieved and a reduction of cooling load of up to 80% can be obtained by PCMs in the low to medium-low temperature range. PCM storage for heating applications can improve operation efficiency from 26% to 66%, depending on specific applications. Solar thermal direct steam generation (DSG) is the most common electricity generation application coupled with PCM storage systems in the high temperature range, due to the capability of PCMs to store and deliver energy at a given constant temperature. The recommendations for future research are also presented which provide insights about where the current research is heading and highlights the challenges that remain to be resolved.

ABSTRACT:The continual increases in global energy demand and greenhouse gas emissions call for more and more utilisation of sustainable energy sources, such as solar energy, biomass energy, and waste heat. Solar thermal energy, the heat of biomass combustion and waste heat may be used to drive a combined heat and power (CHP) system.In recent years, several micro-CHP systems with organic Rankine cycle (ORC) suitable for domestic applications (1-10kW e ) driven by solar thermal, biomass-fired boilers and waste heat resources have been investigated. These ORC-based micro-CHP systems have lower operation pressures and temperatures compared to conventional steam-Rankine cycle CHP systems and hence safer for household applications. However, the lack of commercially available expanders applicable to ORC-based micro-CHP systems has hindered the development of these novel CHP systems. This paper summarizes the findings of the market research for the expanders and discusses the selection and choices of the expanders for ORCbased micro-CHP systems. The working principles and the characteristics of several kinds of expanders, including turbine expanders (i.e., turboexpander), screw expanders, scroll expanders and vane expanders, are introduced and evaluated.

A review is carried out on the development of small-and micro-scale biomass-fuelled